This invention relates to a temperature responsive switch for electrically heated devices, particularly baking ovens. The temperature responsive switch may be of the type which has an electrically heated bimetal, a setting arm and a stationary contact arranged therebetween. These three components which are inserted stackwise on a securing post, such as a hollow rivet, are spaced from one another by electrically insulating discs and project from the post in the same direction, approximately parallel to one another. There is further provided a contact spring which is biased in the direction of the stationary contact and whose fixed end is secured to the movable terminus of the setting arm. The setting arm may be displaced from its mid position by pressure exerted thereon by the bimetal and by a temperature preselector. The bimetal is connected to the electric circuit of the device served by the temperature responsive switch such that when the circuit is closed, current flows through the bimetal.
A temperature responsive switch of the above-outlined known type, if serving, for example, a water heater, provides for heating the water to a preselected temperature and for maintaining the water at that temperature. Such a temperature responsive switch is an output regulator which is controlled exclusively by the current flowing through the bimetal. The heating of the bimetal occurs according to the principle of resistance heating. As soon as the water heater has reached the desired temperature, the bimetal swings the contact spring out of its contacting position into the OFF position. After a certain cooling period which starts as the heating current is interrupted, the contact spring, by virtue of its bias, swings back into the ON position whereby the heating process resumes up to the moment of the successive switch-off. Thus, in this manner, the water heater is maintained essentially at constant heat-up temperatures, and overheating is prevented by the periodic switch-offs. Further, the calorie loss due to the cooling is resupplied after a certain delay during the renewed ON periods. The temperature preselecting device effects a displacement of the movable end of the setting arm and thus causes a change of the position of the stationary end of the contact spring. By virtue of the displacement of the movable end of the setting arm the switch-off effect of the bimetal on the contact spring is made dependent from a variable, predetermined extent of deformation of the bimetal, that is, the holding temperature of the switch may be preselected.
Output regulators of the above-outlined type have the disadvantage that the heat requirement of, for example, the inner space of a baking oven is not taken into account in the regulating process. The switch-off occurs conventionally only as a function of the current flow. The periods of ON position of the output regulator are constant even during the heat-up phase with the result that the heating temperature does not increase sufficiently rapidly. It is, however, an advantage of this type of output regulator that relatively short switching times can be realized. Thus, such output regulators often work with an ON period of only 1 to 2%.
Further, temperature responsive switches are known wherein the bimetal is controlled solely by the actual temperature of the electric device served by the switch. It is a disadvantage of such temperature responsive switches that the regulating periods are too long because of the distance between the switch and the heated environment. Further, the difference between switch-off temperature and switch-on temperature has been found to be very high. The switching behavior of such temperature responsive switches has a relatively high inertia. It is, however, an advantage of this type of temperature responsive switch that regulation may be effected as a function of the necessary heat requirements.